Pest control products developed to control the larval stages (larvicide) of nuisance insect pests are available in several different formulations such as wettable powders, granules, liquids etc. Although said products could be used for controlling nuisance larvae in confined areas such as catch basins, mixing and or weighing of the products would be necessary to deliver the required and correct dose. This process is laborious and not conducive to rapid treatment of numerous catch basins in a given time.
It is desirable to have the larvicide released to the environment in a controlled manner over a period of time thus providing the dose required to cause mortality and reducing the requirement for retreatment. The release rate of the larvicide to a water column can be controlled by the rate at which the carrier materials dissolve in the water column. Thus the selection and mixture of the carrier materials will determine the length of time for which control of nuisance insect larvae is achieved.
Controlled release compositions for treating a population of aquatic organisms in a column of water are disclosed in several U.S. patents issued to Levy, R. (see for example U.S. Pat. Nos. RE37,890, 6,391,328, 6,387,386, 6,350,461, 6,346,262, 6,337,078, 6,335,027, 6,001,382, 5,902,596, 5,885,605, 5,858,386, 5,858,384, 5,846,553 and 5,698,210). Levy describes compositions comprising a pesticide active agent, a carrier component and a coating component. Levy also suggests that the compositions may comprise only a pesticide active agent and a joint-function coating/carrier component. The only materials mentioned as being suitable as a joint-function coating/carrier component in Levy's compositions are polyvinyl alcohol, polyethylene oxide, hydroxypropyl methyl cellulose, cetyl alcohol and stearyl alcohol.
Another controlled release composition for the delivery of pesticides into an aquatic environment is described in Kase, L. E. et al. (Canadian Patent No. 1,225,023). The compositions therein comprise the active agent, a plurality of cork granules and molding plaster. The composition is designed to have a specific gravity of less than 1 so that it will float on the surface of the water.
Solid pesticide compositions in which the pesticide is dispersed in wax are described in U.S. Patents issued to Paulson, P. (see U.S. Pat. Nos. 5,750,128 and 5,505,019). The wax is typically made up of 1-30% microcrystalline wax, 5-40% paraffin oil and 60-95% paraffin wax and 10-25% of flour and/or starch is required to promote the dispersion of the pesticide into the wax. The compositions described in Paulson are designed for the application of pesticides to plants.
Timed released delivery systems in which the treating agent is encapsulated in a biodegradable wax are described in Harvan, D. J. et al. (U.S. Pat. No. 6,004,572). These systems are designed for the application of treating agents to wood and biodegradable waxes suitable for this purpose are microcrystalline waxes having a chain of 20 or more carbon atoms.
There is a need in the art for improved controlled release compositions for the effective delivery of pesticides to aquatic environments.